GEOLOGICAL SURVEY OF THE TERRITOEIES. 



313 



Nortli American Tertiary flora. The examination of this question would 

 demand more details than I can give in this abridged report. 



§4. Stratigraphical Distribution op Fossil Plants in the 

 North American Tertiary Formations. 



Eemarks on this subject cannot be definite and conclusive, the mate- 

 rials obtained being as yet too scanty to furnish valuable information. 

 The table of distribution of the fossil plants of the Miocene of Europe, 

 as established by Heer, as a complement of his admirable work, Flora 

 Tertiaria Helvetica, enumerates nine hundred and twenty species, mark- 

 ing their habitat in three essential divisions, corresponding with Upper 

 Miocene, Middle Miocene, andLower Miocene.* Very few of these species 

 are represented in a single stage or on the same division in the differ- 

 ent geographical sections of the European Tertiary, and, therefore, few, 

 if any, of these species may be considered as leading and characteristic 

 of one of these stages. Of course, one hundred and ninety species could 

 not but afford less decisive indications. The relation indicated by the 

 North American fossil species, now under consideration, with European 

 species, is intimate and evident enough to demonstrate that these plants 

 of ours are of Tertiary age, as it has been already surmised by the com- 

 parisons of the former chapter. Of the one hundred and ninety forms 

 of our leaves enumerated, one-fourth (45) are identical with species of 

 the Miocene of Europe, and one-fifth (33) closely allied to species of the 

 same formation ; but nothing more can be ascertained ; and a reference 

 of these plants, per groups at least, to any stage of the European Terti- 

 ary, would be mere hypothesis. This assertion is proved by the follow- 

 ing table, which indicates from each of our divisions the number of 

 American species identical with species of the different stages of the 

 Miocene of Europe : 



This table is explicit. It shows that species of each of our divisions 

 are nearly equally scattered in the various stages of the Miocene of 

 Europe, and that about one-half of them are identical with species per- 

 taining at least to two of these stages. 



On what kind of evidence are then based the divisions of our own 

 table % On the succession of strata as established by geological obser- 

 vations. The station of some of these strata, especially of those more 

 interesting by the large number of fossil plants obtained: Marshall, 

 Eaton Pass, Evanston, six miles above Spring Oaiion, &c., is in such 

 close connection to Cretaceous strata that it is as yet not possible to point 

 out a line of division, and that they are therefore classed in the category 



* Heer, loc. cit., p. 351-369. The divisions are differently marked for SwitzerlaHfl; 

 France, Germany, and Italy. The essential points only are indicated here. 



